Shale hydration inhibition agent and method of use

ABSTRACT

A water-base drilling fluid for use in drilling wells through a formation containing a shale which swells in the presence of water. The drilling fluid preferably includes: an aqueous based continuous phase, a weight material, and a shale hydration inhibition agent having the formula:
 
H 2 N—R—{OR′} x —Y.[H + B − ] d 
 
in which R and R′ are alkylene groups having 1 to 6 carbon atom and x is a value from about 1 to about 25. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group. The acid H + B −  is a protic acid selected from the group consisting of inorganic acids and organic acids, illustrative examples of which include: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. The shale hydration inhibition agent should be present in sufficient concentration to reduce the swelling of the shale. Also inclusive of the present invention is a method of reducing the swelling of shale clay encountered during the drilling of a subterranean well, the method comprising circulating in the well a water-base drilling fluid formulated in accordance with the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 09/709,962, filed Nov. 10, 2000, now U.S. Pat. No. 6,484,821 and a continuation-in-part of U.S. patent application Ser. No. 09/884,013, filed Jun. 18, 2001, now U.S. Pat. No. 6,609,578. U.S. patent application Ser. No. 09/884,013, filed Jun. 18, 2001, now U.S. Pat. No. 6,609,578 is also a continuation-in-part of U.S. patent application Ser. No. 09/709,962, filed Nov. 10, 2000, now U.S. Pat. No. 6,484,821, and a continuation-in-part of U.S. patent application Ser. No. 09/503,558, filed Feb. 11, 2000 now U.S. Pat. No. 6,247,543.

BACKGROUND OF THE INVENTION

In rotary drilling of subterranean wells numerous functions and characteristics are expected of a drilling fluid. A drilling fluid should circulate throughout the well and carry cuttings from beneath the bit, transport the cuttings up the annulus, and allow their separation at the surface. At the same time, the drilling fluid is expected to cool and clean the drill bit, reduce friction between the drill string and the sides of the hole, and maintain stability in the borehole's uncased sections. The drilling fluid should also form a thin, low permeability filter cake that seals openings in formations penetrated by the bit and act to reduce the unwanted influx of formation fluids from permeable rocks.

Drilling fluids are typically classified according to their base material. In oil base fluids, solid particles are suspended in oil, and water or brine may be emulsified with the oil. The oil is typically the continuous phase. In water base fluids, solid particles are suspended in water or brine, and oil may be emulsified in the water. The water is typically the continuous phase. Pneumatic fluids are a third class of drilling fluids in which a high velocity stream of air or natural gas removes drill cuttings.

Three types of solids are usually found in water base drilling fluids: 1) clays and organic colloids added to provide necessary viscosity and filtration properties; 2) heavy minerals whose function is to increase the drilling fluid's density; and 3) formation solids that become dispersed in the drilling fluid during the drilling operation.

The formation solids that become dispersed in a drilling fluid are typically the cuttings produced by the drill bit's action and the solids produced by borehole instability. Where the formation solids are clay minerals that swell, the presence of either type of formation solids in the drilling fluid can greatly increase drilling time and costs.

Clay minerals are generally crystalline in nature. The structure of a clay's crystals determines its properties. Typically, clays have a flaky, mica-type structure. Clay flakes are made up of a number of crystal platelets stacked face-to-face. Each platelet is called a unit layer, and the surfaces of the unit layer are called basal surfaces.

A unit layer is composed of multiple sheets. One sheet is called the octahedral sheet, it is composed of either aluminum or magnesium atoms octahedrally coordinated with the oxygen atoms of hydroxyls. Another sheet is called the tetrahedral sheet. The tetrahedral sheet consists of silicon atoms tetrahedrally coordinated with oxygen atoms.

Sheets within a unit layer link together by sharing oxygen atoms. When this linking occurs between one octahedral and one tetrahedral sheet, one basal surface consists of exposed oxygen atoms while the other basal surface has exposed hydroxyls. It is also quite common for two tetrahedral sheets to bond with one octahedral sheet by sharing oxygen atoms. The resulting structure, known as the Hoffman structure, has an octahedral sheet that is sandwiched between the two tetrahedral sheets. As a result, both basal surfaces in a Hoffman structure are composed of exposed oxygen atoms.

The unit layers stack together face-to-face and are held in place by weak attractive forces. The distance between corresponding planes in adjacent unit layers is called the c-spacing. A clay crystal structure with a unit layer consisting of three sheets typically has a c-spacing of about 9.5×10⁻⁷ mm.

In clay mineral crystals, atoms having different valences commonly will be positioned within the sheets of the structure to create a negative potential at the crystal surface. In that case, a cation is adsorbed on the surface. These adsorbed cations are called exchangeable cations because they may chemically trade places with other cations when the clay crystal is suspended in water. In addition, ions may also be adsorbed on the clay crystal edges and exchange with other ions in the water.

The type of substitutions occurring within the clay crystal structure and the exchangeable cations adsorbed on the crystal surface greatly affect clay swelling, a property of primary importance in the drilling fluid industry. Clay swelling is a phenomenon in which water molecules surround a clay crystal structure and position themselves to increase the structure's c-spacing thus resulting in an increase in volume. Two types of swelling may occur.

Surface hydration is one type of swelling in which water molecules are adsorbed on crystal surfaces. Hydrogen bonding holds a layer of water molecules to the oxygen atoms exposed on the crystal surfaces. Subsequent layers of water molecules align to form a quasi-crystalline structure between unit layers which results in an increased c-spacing. Virtually all types of clays swell in this manner.

Osmotic swelling is a second type of swelling. Where the concentration of cations between unit layers in a clay mineral is higher than the cation concentration in the surrounding water, water is osmotically drawn between the unit layers and the c-spacing is increased. Osmotic swelling results in larger overall volume increases than surface hydration. However, only certain clays, like sodium montmorillonite, swell in this manner.

Exchangeable cations found in clay minerals are reported to have a significant impact on the amount of swelling that takes place. The exchangeable cations compete with water molecules for the available reactive sites in the clay structure. Generally cations with high valences are more strongly adsorbed than ones with low valences. Thus, clays with low valence exchangeable cations will swell more than clays whose exchangeable cations have high valences.

In the North Sea and the United States Gulf Coast, drillers commonly encounter argillaceous sediments in which the predominant clay mineral is sodium montmorillonite (commonly called “gumbo shale”). Sodium cations are predominately the exchangeable cations in gumbo shale. As the sodium cation has a low positive valence (i.e. formally a +1 valence), it easily disperses into water. Consequently, gumbo shale is notorious for its swelling.

Clay swelling during the drilling of a subterranean well can have a tremendous adverse impact on drilling operations. The overall increase in bulk volume accompanying clay swelling impedes removal of cuttings from beneath the drill bit, increases friction between the drill string and the sides of the borehole, and inhibits formation of the thin filter cake that seals formations. Clay swelling can also create other drilling problems such as loss of circulation or stuck pipe that slow drilling and increase drilling costs. Thus, given the frequency in which gumbo shale is encountered in drilling subterranean wells, the development of a substance and method for reducing clay swelling remains a continuing challenge in the oil and gas exploration industry.

One method to reduce clay swelling is to use salts in drilling fluids. Salts generally reduce the swelling of clays. However, salts flocculate the clays resulting in both high fluid losses and an almost complete loss of thixotropy. Further, increasing salinity often decreases the functional characteristics of drilling fluid additives.

Another method for controlling clay swelling is to use organic shale inhibitor molecules in drilling fluids. It is believed that the organic shale inhibitor molecules are adsorbed on the surfaces of clays with the added organic shale inhibitor competing with water molecules for clay reactive sites and thus serve to reduce clay swelling.

Organic shale inhibitor molecules can be either cationic, anionic, or nonionic. Cationic organic shale inhibitors dissociate into organic cations and inorganic anions, while anionic organic shale inhibitors dissociate into inorganic cations and organic anions. Nonionic organic shale inhibitor molecules do not dissociate.

It is important that the driller of subterranean wells be able to control the rheological properties of drilling fluids by using additives, including organic shale inhibitor molecules. In the oil and gas industry today it is desirable that additives work both onshore and offshore and in fresh and salt water environments. In addition, as drilling operations impact on plant and animal life, drilling fluid additives should have low toxicity levels and should be easy to handle and to use to minimize the dangers of environmental pollution and harm to operators. Any drilling fluid additive should also provide desirable results but should not inhibit the desired performance of other additives. The development of such additives will help the oil and gas industry to satisfy the long felt need for superior drilling fluid additives which act to control the swelling of the clay and drilled formations without adversely effecting the rheological properties of drilling fluids. The present invention addresses this need.

SUMMARY OF THE INVENTION

The present invention is generally directed to a water-base drilling fluid for use in drilling wells through a formation containing a shale clay which swells in the presence of water. The inventive drilling fluid includes: an aqueous based continuous phase; a weight material; and a shale hydration inhibition agent. Preferably the shale hydration inhibition agent has a formula: H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d) in which R and R′ are alkylene groups having 1 to 6 carbon atoms and x is a value from about 1 to about 25. The Y group may be an amine or alkoxy group, preferably a primary amine or a methoxy group. The H⁺B⁻ may be a Bronsted-Lowery protic acid that may be either organic or inorganic in nature. The value of d varies greatly depending upon the amount of acid added, the pKa of the acid and the pKb of the amine base and the overall pH of the drilling mud. Typically the value of d is less than or equal to 2. The shale hydration inhibition agent should be present in a sufficient concentration to reduce the swelling of gumbo shale or other hydrophilic rocks encountered during the drilling of wells with the inventive drilling fluid. The alkylene groups, R and R′ may be the same or they may be different from each other and may include a mixture of alkylene groups. That is to say that R and R′ may have a mixture of a different number of carbon atoms.

Another illustrative embodiment of the present invention is a water-base drilling fluid as described above in which the shale hydration inhibition agent may be selected from: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d) H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂ [H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) and mixtures of these. The H⁺B⁻ may be a Bronsted-Lowery protic acid that may be either organic or inorganic in nature. The value of d varies greatly depending upon the amount of acid added, the pKa of the acid and the pKb of the amine base and the overall pH of the drilling mud. Typically the value of d is less than or equal to 2. As with the previously described drilling fluid, the hydration inhibition agent should be present in the drilling fluid in sufficient concentrations to reduce the swelling of the clay.

Further the shale hydration inhibition agents should preferably be characterized by a relatively low toxicity as measured by the Mysid shrimp test and compatibility with anionic drilling fluid components that may be present in the drilling fluid. The United States Environmental Protection Agency has specified a Mysid shrimp bioassay as the means for assessing marine aquatic toxicity of drilling fluids. A detailed account of the procedure for measuring toxicity of drilling fluids is described in Duke, T. W., Parrish, P. R.; “Acute Toxicity of Eight Laboratory Prepared Generic Drilling Fluids to Mysids (Mysidopsis)” 1984 EPA-600/3-84-067, the subject matter of which is incorporated herein by reference.

For purposes of understanding the term “low toxicity” within the context of this application, the term refers to a drilling fluid with an LC50 of greater than 30,000 ppm by the Mysid shrimp test. Although 30,000 has been the number used for purposes of evaluation it should not be considered a limitation on the scope of this invention. Rather, the tests provide a context for use of the term “low toxicity” as used in the present invention which will be readily understood by those with ordinary skill in the art. Other LC50 values may be viable in various environmental settings. An LC50 value of greater than 30,000 has been equated to an “environmentally compatible” product.

The drilling fluids of the present invention preferably have an aqueous based continuous phase selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof. In addition such a drilling fluid may further contain a fluid loss control agent selected from the group of organic synthetic polymers, biopolymers and sized particle diatomaceous earth, and mixtures thereof. It is in the scope of the present invention that the drilling fluid may further contain an encapsulating agent such as one preferably selected from the group consisting of organic and inorganic polymers and mixtures thereof. A weight material may also be included in the formulation of the drilling fluid with the weighting agent preferably being selected from the group of barite, hematite, iron oxide, calcium carbonate, magnesium carbonate, soluble and insoluble organic and inorganic salts, and combinations thereof.

Also inclusive within the present invention is a method of reducing the swelling of shale clay in a well comprising circulating in the well a water-base drilling fluid formulated in accordance with the present invention.

These and other features of the present invention are more fully set forth in the following description of illustrative embodiments of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is directed to a water-base drilling fluid for use in drilling wells through a formation containing a shale which swells in the presence of water. Generally the drilling fluid of the present invention includes a weight material, a shale hydration inhibition agent and an aqueous continuous phase. As disclosed below, the drilling fluids of the present invention may also include additional components, such as fluid loss control agents, bridging agents, lubricants, anti-bit balling agents, corrosion inhibition agents, surfactants and suspending agents and the like which may be added to an aqueous based drilling fluid.

The shale hydration inhibition agent of the present invention is preferably the protic acid salt of polyoxyalkylenediamines and monoamines which inhibits the swelling of shale that may be encountered during the drilling process. Preferably the alkylene group is a straight chain alkylene, that may be the same (i.e. all ethylene units) different (i.e. methylene, ethylene, propylene, etc.) or mixtures of alkylene groups. However, branched alkylene group can also be used. While a variety of members of this group may serve as shale inhibition agents, we have found that compounds having the general formula H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d) in which R and R′ are alkylene groups having 1 to 6 carbon atoms and in which the R and R′ groups may be the same or different from each other or mixtures of alkylene groups are effective as shale hydration inhibitors. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group.

The H⁺B⁻ is a Bronsted-Lowery protic acid that may be either organic or inorganic in nature. The value of d varies greatly depending upon the amount of acid added, the pKa of the acid and the pKb of the amine base and the overall pH of the drilling mud. Typically the value of d is less than or equal to 2. The important property in the selection of the acid is that it be capable of at least partially protonating one or more of the proton accepting moieties of the amine compound. Illustrative examples of suitable protic acids include hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. One of skill in the art should understand and appreciate that the conjugate base B⁻ in the shale inhibitor formulation shown above will be directly influenced by the selection of the acid or mixture of acids utilized to neutralize the amine starting materials. Further it also should be appreciated that the concentration of the amine salt verse that of the free amine depends upon many factors including the pKa of the acid, the pKb of the base and the pH of the mud formulation. Given such information however, one of skill in the art should be able to readily be able to calculate the relative ratios of unprotonated amine to protonated amine in the mud formulation.

The value of x has been found to be a factor in the ability of the shale hydration inhibitors to carry out their desired role. The value of x may be a whole number or fractional number that reflects the average molecular weight of the compound. In one embodiment of the present invention x may have a value from about 1 to about 25 and preferably have a value between about 1 and about 10.

The important property in the selection of the shale inhibition agents of the present invention is that the selected compounds or mixture of compounds should provide effective inhibition of shale hydration when the shale is exposed to the drilling fluid.

In one preferred illustrative embodiment of the present invention the shale hydration inhibition agent may be selected from: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d)  H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂.[H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) and mixtures of these, and similar compounds.

The H⁺B⁻ is a Bronsted-Lowery protic acid that may be either organic or inorganic in nature. The value of d varies greatly depending upon the amount of acid added, the pKa of the acid and the pKb of the amine base and the overall pH of the drilling mud. Typically the value of d is less than or equal to 2. The important property in the selection of the acid is that it be capable of at least partially protonating one or more of the proton accepting moieties of the amine compound. Illustrative examples of suitable protic acids include hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. One of skill in the art should understand and appreciate that the conjugate base B⁻ in the shale inhibitor formulation shown above will be directly influenced by the selection of the acid or mixture of acids utilized to neutralize the amine starting materials. Further it also should be appreciated that the concentration of the amine salt versus that of the free amine depends upon many factors including the pKa of the acid, the pKb of the base and the pH of the mud formulation. Given such information however, one of skill in the art should be able to readily calculate the relative ratios of unprotonated amine to protonated amine in the mud formulation.

The shale hydration inhibition agent should be present in sufficient concentration to reduce either or both the surface hydration based swelling and/or the osmotic based swelling of the shale. The exact amount of the shale hydration inhibition agent present in a particular drilling fluid formulation can be determined by a trial and error method of testing the combination of drilling fluid and shale formation encountered. Generally however, the shale hydration inhibition agent of the present invention may be used in drilling fluids in a concentration from about 1 to about 18 pounds per barrel (lbs/bbl or ppb) and more preferably in a concentration from about 2 to about 12 pounds per barrel of drilling fluid.

In addition to the inhibition of shale hydration by the shale hydration inhibition agent, other properties are beneficially achieved. In particular it has been found that the shale hydration inhibition agents of the present invention may also be further characterized by their compatibility with other drilling fluid components, tolerant to contaminants, temperature stability and low toxicity. These factors contribute to the concept that the shale hydration inhibition agents of the present invention may have broad application both in land based drilling operations as well as offshore drilling operations.

The drilling fluids of the present invention include a weight material in order to increase the density of the fluid. The primary purpose for such weighting materials is to increase the density of the drilling fluid so as to prevent kick-backs and blow-outs. One of skill in the art should know and understand that the prevention of kick-backs and blow-outs is important to the safe day to day operations of a drilling rig. Thus the weight material is added to the drilling fluid in a functionally effective amount largely dependent on the nature of the formation being drilled.

Weight materials suitable for use in the formulation of the drilling fluids of the present invention may be generally selected from any type of weighting materials be it in solid, particulate form, suspended in solution, dissolved in the aqueous phase as part of the preparation process or added afterward during drilling. It is preferred that the weight material be selected from the group including barite, hematite, iron oxide, calcium carbonate, magnesium carbonate, organic and inorganic salts, and mixtures and combinations of these compounds and similar such weight materials that may be utilized in the formulation of drilling fluids.

The aqueous based continuous phase may generally be any water based fluid phase that is compatible with the formulation of a drilling fluid and is compatible with the shale hydration inhibition agents disclosed herein. In one preferred embodiment, the aqueous based continuous phase is selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof. The amount of the aqueous based continuous phase should be sufficient to form a water based drilling fluid. This amount may range from nearly 100% of the drilling fluid to less than 30% of the drilling fluid by volume. Preferably, the aqueous based continuous phase is from about 95 to about 30% by volume and preferably from about 90 to about 40% by volume of the drilling fluid.

In addition to the other components previously noted, materials generically referred to as gelling materials, thinners, and fluid loss control agents, are optionally added to water base drilling fluid formulations. Of these additional materials, each can be added to the formulation in a concentration as rheologically and functionally required by drilling conditions. Typical gelling materials used in aqueous based drilling fluids are bentonite, sepiolite, clay, attapulgite clay, anionic high-molecular weight polymer and biopolymers.

Thinners such as lignosulfonates are also often added to water-base drilling fluids. Typically lignosulfonates, modified lignosulfonates, polyphosphates and tannins are added. In other embodiments, low molecular weight polyacrylates can also be added as thinners. Thinners are added to a drilling fluid to reduce flow resistance and control gelation tendencies. Other functions performed by thinners include reducing filtration and filter cake thickness, counteracting the effects of salts, minimizing the effects of water on the formations drilled, emulsifying oil in water, and stabilizing mud properties at elevated temperatures.

A variety of fluid loss control agents may be added to the drilling fluids of the present invention that are generally selected from a group consisting of synthetic organic polymers, biopolymers, and mixtures thereof. The fluid loss control agents such as modified lignite, polymers, modified starches and modified celluloses may also be added to the water base drilling fluid system of this invention. In one embodiment it is preferred that the additives of the invention should be selected to have low toxicity and to be compatible with common anionic drilling fluid additives such as polyanionic carboxymethylcellulose (PAC or CMC), polyacrylates, partially-hydrolyzed polyacrylamides (PHPA), lignosulfonates, xanthan gum, mixtures of these and the like.

The drilling fluid of the present invention may further contain an encapsulating agent generally selected from the group consisting of synthetic organic, inorganic and bio-polymers and mixtures thereof. The role of the encapsulating agent is to absorb at multiple points along the chain onto the clay particles, thus binding the particles together and encapsulating the cuttings. These encapsulating agents help improve the removal of cuttings with less dispersion of the cuttings into the drilling fluids. The encapsulating agents may be anionic, cationic, amphoteric, or non-ionic in nature.

Other additives that could be present in the drilling fluids of the present invention include products such as lubricants, penetration rate enhancers, defoamers, corrosion inhibitors and loss circulation products. Such compounds should be known to one of ordinary skill in the art of formulating aqueous based drilling fluids.

The use of the above disclosed drilling fluids is contemplated as being within the scope of the present invention. Such use would be conventional to the art of drilling subterranean wells and one having skill in the art should appreciate such processes and applications.

Thus one embodiment of the present invention may include a method of reducing the swelling of shale clay in a well, involving circulating in the well a water-base drilling fluid formulated in accordance with the present disclosure. Preferably such a fluid would include: an aqueous based continuous phase, a weight material and a shale hydration inhibition agent having the formula: H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d)

As noted above, R and R′ are alkylene groups having 1 to 6 carbon atoms and x should have a value from about 1 to about 25. Preferably x has a value between about 1 and about 10. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group. Further the drilling fluid should include the shale hydration inhibition agent present in sufficient concentration to reduce the swelling of the clay encountered in the well drilling process.

The H⁺B⁻ is a Bronsted-Lowery protic acid that may be either organic or inorganic in nature. The value of d varies greatly depending upon the amount of acid added, the pKa of the acid and the pKb of the amine base and the overall pH of the drilling mud. Typically the value of d is less than or equal to 2. The important property in the selection of the acid is that it be capable of at least partially protonating one or more of the proton accepting moieties of the amine compound. Illustrative examples of suitable protic acids include hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. One of skill in the art should understand and appreciate that the conjugate base B⁻ in the shale inhibitor formulation shown above will be directly influenced by the selection of the acid or mixture of acids utilized to neutralize the amine starting materials. Further it also should be appreciated that the concentration of the amine salt verse that of the free amine depends upon many factors including the pKa of the acid, the pKb of the base and the pH of the mud formulation. Given such information however, one of skill in the art should be able to readily be able to calculate the relative ratios of unprotonated amine to protonated amine in the mud formulation.

Another embodiment of the present inventive method includes a method of reducing the swelling of shale in a well comprising circulation in the well, a water-base fluid formulated in accordance with the teachings of this disclosure.

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the invention.

Unless otherwise stated, all starting materials are commercially available and standard laboratory techniques and equipment are utilized. The tests were conducted in accordance with the procedures in API Bulletin RP 13B-2, 1990. The following abbreviations are sometimes used in describing the results discussed in the examples:

“PV” is plastic viscosity (CPS) which is one variable used in the calculation of viscosity characteristics of a drilling fluid.

“YP” is yield point (lbs/100 ft²) which is another variable used in the calculation of viscosity characteristics of drilling fluids.

“GELS” (lbs/100 ft²) is a measure of the suspending characteristics and the thixotropic properties of a drilling fluid.

“F/L” is API fluid loss and is a measure of fluid loss in milliliters of drilling fluid at 100 psi.

Example 1

In the present example, a variety of polyoxyalkylamines were tested to determine if they would function as shale inhibitors.

The following test was conducted to demonstrate the maximum amount of API bentonite that can be inhibited by a single 10 pounds per barrel (ppb) treatment of shale inhibitor of the present invention over a period of days. This test procedure uses pint jars that are filled with one barrel equivalent of tap water and about 10 ppb of a shale inhibitor. Tap water was used as a control sample. All samples were adjusted to at least a pH of 9 and treated with about 10 ppb portion of M-I GEL (bentonite) at a medium shear rate. After stirring for about 30 minutes, the rheologies were measured and then the samples were heat aged overnight at about 150° F. After the samples were cooled their rheologies and pH values were measured and recorded. All samples were then adjusted, to a pH value of at least about 9 before treating them again with bentonite as previously described.

This procedure was carried out for each sample until all of the samples were too thick to measure. Tables 1 to 6 present data illustrating the shale inhibition effects of the present invention by the daily addition of bentonite in tap water treated with various inhibitors of present invention. As used below, Jeffamine D-230 is a polyoxyalkyldiamine available from Huntsman Chemicals and S-2053 is a polyoxyethylenediamine available from Champion Chemicals.

TABLE 1 600 RPM Rheology Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20  5 40 30  6 43 40  8 44 50 10 43 60 13 29 70 20 49 80 29 79 90 55 141  100 98   300+  110 169  — 120   300+  —

TABLE 2 300 RPM Rheology Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20 3 33 30 3 38 40 4 36 50 5 30 60 7 14 70 10 25 80 15 42 90 30 76 100 52 290 110 94 — 120 186 —

TABLE 3 3 RPM Rheology Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20 1 5 30 1 9 40 1 9 50 0 5 60 1 1 70 1 1 80 1 1 90 1 2 100 1 11 110 8 — 120 4 —

TABLE 4 10 Min. GELS Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20 1 5 30 1 9 40 1 9 50 1 7 60 1 1 70 2 2 80 1 2 90 1 8 100 1 53 110 9 — 120 40 —

TABLE 5 Plastic Viscosity Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20 2 7 30 3 5 40 4 8 50 5 13 60 6 15 70 10 24 80 14 37 90 25 65 100 46 — 110 75 — 120 — —

TABLE 6 Yield Point Data Heat Aged Data - pH 11.0-11.8 10 ppb M-I Gel Jeffamine D-230 S-2053 20 1 26 30 0 33 40 0 28 50 0 17 60 1 −1 70 0 1 80 1 5 90 5 11 100 6 — 110 16 — 120 — —

Upon review of the above data in Tables 1-6, one of skill in the art can see that the dioxyethylenediamine product (S-2053) gives good shale inhibiting characteristics and properties.

Example 2

The evaluation of the dioxyethylenediamine product that has been neutralized in the test fluid with hydrochloric acid to a pH value of about 9.0 has been conducted. The results in the tables 7-12 show the performance of the drilling fluids of this invention at a pH value of about 9.0.

TABLE 7 600 RPM Rheology Data Heat Aged Data- pH 9.0 10 ppb M-I Gel Jeffamine D-230 S-2053 20 4 4 30 4 4 40 6 6 50 7 6 60 8 7 70 9 9 80 13 13 90 16 14 100 15 15 110 21 19 120 25 23 130 31 28 140 44 36 150 — — 160 180 82 170 — 204

TABLE 8 300 RPM Rheology Data Heat Aged Data - pH 9.0 10 ppb M-I Gel Jeffamine D-230 S-2053 20 2 2 30 3 3 40 3 3 50 3 3 60 4 4 70 5 6 80 8 8 90 11 9 100 10 10 110 14 13 120 17 15 130 19 19 140 26 25 140 — — 160 130 62 170 — 150

TABLE 9 3 RPM Rheology Data Heat Aged Data - pH 9.0 10 ppb M-I Gel Jeffamine D-230 S-2053 20 1 1 30 1 1 40 1 1 50 1 1 60 1 1 70 2 2 80 3 3 90 5 4 100 4 3 110 7 6 120 8 7 130 7 9 140 7 14 150 — — 160 65 35 170 — 90

TABLE 10 10 MIN GELS Data Heat Aged Data - pH 9.0 10 ppb M-I GEL Jeffamine D-230 S-2053 20 0 0 30 0 0 40 0 0 50 0 0 60 (−1) 1 70 0 3 80 0 3 90 6 4 100 5 5 110 7 7 120 9 7 130 12 10 140 8 14 150 — — 160 80 42 170 — 90

TABLE 11 Plastic Viscosity Data Heat Aged Data - pH 9.0 10 ppb M-I Gel Jeffamine D-230 S-2053 20 2 2 30 1 1 40 3 3 50 4 3 60 4 3 70 4 3 80 5 5 90 5 5 100 5 5 110 7 6 120 8 8 130 12 9 140 18 11 150 — — 160 50 20 170 — 54

TABLE 12 Yield Point Data Heat Aged Data - pH 9.0 10 ppb M-I Gel Jeffamine D-230 S-2053 20 0 0 30 2 2 40 0 0 50 −1 0 60 0 1 70 1 3 80 3 3 90 6 4 100 5 5 110 7 7 120 9 7 130 7 10 140 8 14 150 — — 160 80 42 170 — 96

Upon review of the above data in Tables 7-12, one of skill in the art can see that the dioxyethylenediamine product (S-2053) gives good shale inhibiting properties at a pH value of about 9.0.

Example 3

To further demonstrate the performance of the drilling fluids formulated in accordance with the teachings of this invention, a test using a bulk hardness tester was conducted. A BP Bulk Hardness Tester is a device designed to give an assessment of the hardness of shale cuttings exposed to drilling fluids which in turn can be related to the inhibiting properties of the drilling fluid being evaluated. In this test, shale cutting are hot rolled in the test drilling fluid at 150° F. for 16 hours. Shale cuttings are screened and then placed into a BP Bulk Hardness Tester. The equipment is closed and using a torque wrench the force used to extrude the cuttings through a plate with holes in it is recorded. Depending on the hydration state and hardness of the cuttings and the drilling fluid used, a plateau region in torque is reached as extrusion of the cuttings begins to take place. Alternatively, the torque may continue to rise which tends to occur with harder cuttings samples. Therefore, the higher the torque number obtained, the more inhibative the drilling fluid system is considered. Illustrative data obtained using three different concentrations of each test product with three different cuttings are given below.

TABLE 13 Bulk Hardness Data Arne Cuttings No. S-2053 S-2053 S-2053 D-230 D-230 D-230 Turns @ 1% @ 3% @ 5% @ 1% @ 3% @ 5% 0 1 2 3 4 5 10 10 6 10 20 7 10 15 10 20 70 110 8 50 50 50 80 160 180 9 50 70 70 100 200 240 10 60 80 80 120 230 260 11 60 80 80 130 240 290 12 60 80 85 130 250 310 13 60 90 85 140 290 330 14 65 90 100 170 15 200 150 16

TABLE 14 Bulk Hardness Data Foss Eikeland Clay No. S-2053 S-2053 S-2053 D-230 D-230 D-230 Turns @ 1% @ 3% @ 5% @ 1% @ 3% @ 5% 0 1 2 3 4 5 10 10 6 10 10 10 20 20 7 15 20 20 50 50 8 10 40 70 30 280 290 9 20 230 310 200 10 80 330 11 230 12 260 13 290 14 15

TABLE 15 Bulk Hardness Data Oxford Clay No. S-2053 S-2053 S-2053 D-230 D-230 D-230 Turns @ 1% @ 3% @ 5% @ 1% @ 3% @ 5% 0 1 2 3 10 10 10 4 10 15 20 20 5 10 10 20 35 25 6 15 20 50 70 40 7 10 50 70 180 250 100 8 50 160 190 9 100 205 200 10 130 210 220 11 130 210 220 12 120 200 210 13 130 210 210 14 150 220 240 15 250 16

Upon review of the above data in Tables 13-15, one skilled in the art should observe that drilling fluids formulated according to the teachings of this invention prevent the hydration of various types of shale clays and thus are likely to provide good performance in drilling subterranean wells encountering such shale clays.

Example 4

In the present example, RMR 8-38 is a polyoxyethylenepropylenediamine available from Champion Chemicals was tested to determine if it would function as a shale inhibitor as described in the present invention. Pint jars were filled with about one barrel equivalent of tap water and the test sample, the pH value was adjusted to a value of about 9 and treated with about 50 ppb portion M-I GEL (bentonite) at a medium shear rate. After stirring for about 30 minutes, the rheologies were measured and then the samples were heat aged overnight at about 150° F. After the samples were rolled their rheologies and pHs were recorded. The following data (Table 16) is representative of how the rheologies are affected by the addition of about 50 ppb of bentonite in tap water treated with shale inhibitors of this invention.

TABLE 16 Bentonite Inhibition - 50 gms M-I GEL Heat Aged Data - pH @ 8.0 600 300 200 100 6 3 D-230 5 3 2 2 1 1 S-2053 5 3 2 2 1 1 RMR 8-38 5 3 2 2 1 1 Gels Gels 10 sec 10 min PV VP PH D-230 1 1 2 1 7.7 S-2053 1 1 2 1 7.6 RMR 8-38 1 1 2 1 7.0

The results above show the superior shale inhibition performance of drilling fluids formulated in accordance with the teachings of the present invention.

Example 5

Dispersion and BP Bulk Hardness Tests were run with Arne cuttings by hot rolling about 40.0 g of cuttings having a US standard mesh size of about 5-8. in approximately one-barrel equivalent of a field mud for about 16 hours at about 150° F. The field mud was a lignosulfonate water based mud, 18.13 pounds per gallon weighed with barite from Murphy E&P, Vermilion Parish, La. After hot rolling, the cuttings were screened using a US standard 20 mesh screen and washed with 10% KCl aqueous solution and dried to obtain the percentage recovered. The same procedure was used to obtain cuttings for the BP Bulk Hardness Tester as described previously. The following results are illustrative of the data from this evaluation and are given in Tables 17 and 18.

TABLE 17 Shale Dispersion Test Arne Cuttings (4.6-8.0 mm) % Total Recovered Base Field Mud  <5 Base Mud + Jeffamine D230 >90 Base Mud + Special Products S-2053 >90

TABLE 18 Bulk Hardness Data Base Mud + Base Mud + No. Turns Base Mud 3% D-230 3% S-2053 1 ** — — 2 ** — — 3 ** — — 4 ** 10 — 5 ** 15 10 6 ** 40 20 7 ** 80 60 8 ** 90 70 9 ** 100 80 10 ** 105 80 11 ** 120 90 12 ** 140 90 13 ** 150 120 14 ** 210 180 15 ** ** Indicates that the cuttings were dissolved and test could not be run.

Rheology Data Heat Aged Data - Initial Base Mud Base Mud + 3% 2053 Rheology @ 600 rpm 158 150 Rheology @ 300 rpm 92 84 Rheology @ 3 rpm 5 4 Gels 5 sec. 7 5 10 min. 15 10 Plastic Viscosity 66 66 Yield Point 26 18 pH 9 11

Rheology Data Heat Aged Data After Dispersion Test - Arne Cuttings (40 g) Base Mud Base Mud + 3% 2053 Rheology @ 600 rpm 300 165 Rheo1ogy @ 300 rpm 270 95 Rheology @ 3 rpm 50 5 Gels 5 sec. 57 8 10 min. 134 15 Plastic Viscosity — 70 Yield Point — 25 pH 9.1 12.7

Upon review of the above data in Tables 17-18 and the rheology data, one skilled in the art should observe that a field mud formulated so that it becomes a drilling fluid formulated according to the teachings of this invention prevent the hydration of various types of shale clays and thus are likely to provide good performance in drilling subterranean wells encountering such shale clays.

Example 6

In this procedure a pint jar was filled with one barrel equivalent of tap water and test sample, adjusted the pH to at least 9 and treated with a 50 ppb portion M-I GEL (bentonite) at a medium shear rate. After stirring for 30 minutes, the rheologies were measured and then the samples were heat aged overnight at 150° F. After the samples were cooled their rheologies and pHs were recorded. The following data is representative of how the rheologies are affected by the addition of the 50 ppb of bentonite in tap water treated with the experimental inhibitors.

Bentonite Hydration Study Initial Rheology RPM Additive 600 300 200 100 6 3 Jeffamine 52 33 25 17 5 4 M-600 * If 600 RPM reading is greater than 300, no further readings were taken. Jeffamine M-600 is polyalkoxyalkene amine from Huntsman Chemicals.

Bentonite Hydration Study Initial Rheology Gels Gels Additive 10 sec. 10 min. PV YP pH Jeffamine 11 25 19 14 11.1 M-600

Bentonite Hydration Study Heat Aged Rheology (150° F.) RPM Additive 600 300 200 100 6 3 Jeffamine 40 24 17 10 1 1 M-600 * If 600 RPM reading is greater than 300, no further readings were taken.

Bentonite Hydration Study Heat Aged Rheology (150° F.) Gels Gels Additive 10 sec. 10 min. PV YP pH Jeffamine 1 1 16 8 11.1 M-600

The above results should show to one of skill in the art that Jeffamine M-600 a compound having the formula NH₂—CH(CH₃)—CH₂—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃

-   -   and within the scope of this invention performed well as shale         hydration inhibitors.

Example 7

The following test was conducted to demonstrate the maximum amount of API bentonite that can be inhibited by a single 10 pounds per barrel (ppb) treatment of shale inhibitor of the present invention over a period of days. This test procedure uses pint jars that are filled with one barrel equivalent of tap water and 10 ppb of a shale inhibitor. Tap water was used as a control sample. All samples were adjusted to at least a pH of 9 and treated with a 10 ppb portion of M-I GEL (bentonite) at a medium shear rate. After stirring for 30 minutes, the rheologies were measured and then the samples were heat aged overnight at 150° F. After the samples were cooled their rheologies and pHs were recorded. All samples were then adjusted to at least a pH 9 before treating them again with bentonite as previously described. This procedure was carried out for each sample until all were too thick to measure. The following tables present representative data that shows shale inhibition effects of the present invention by the daily addition of bentonite in tap water treated with the inhibitors indicated at the top of each column.

TABLE 19 600 rpm Rheologies - Heat Aged (150° F.) Bentonite Jeffamine (lb/bbl) Base M-600 30 162 18 40  300* 35 50 — 74 60 — 146 70 — 259 80 — — 90 — — *If 600 RPM reading is greater than 300, no further readings were taken.

TABLE 20 300 rpm Rheologies - Heat Aged (150° F.) Bentonite Jeffamine (lb/bbl) Base M-600 30 112 9 40 — 18 50 — 41 60 — 71 70 — 121 80 — — 90 — —

TABLE 21 3 rpm Rheologies - Heat Aged (150°) Bentonite Jeffamine (lb/bbl) Base M-600 30  8 0 40 132 0 50 — 0 60 — 0 70 — 0 80 — — 90 — —

TABLE 22 10 Min Gels - Heat Aged (150°) Bentonite Jeffamine (lb/bbl) Base M-600 30  30 0 40 184 0 50 — 0 60 — 0 70 — 3 80 — — 90 — —

TABLE 23 Plastic Viscosity - Heat Aged (150°) Bentonite Jeffamine (lb/bbl) Base M-600 30 50 9 40 — 16 50 — 33 60 — 75 70 — 138 80 — — 90 — —

TABLE 24 Yield Point - Heat Aged (150°) Bentonite Jeffamine (lb/bbl) Base M-600 30 62 1 40 — 1 50 — 8 60 — 4 70 — 17  80 — — 90 — —

Upon review of the above rheology data, one of skill in the art should appreciate and see that Jeffamine M-600 performs as a shale hydration inhibitor within the scope of the present invention.

Example 8

The following tests were conducted to demonstrate that the shale inhibiting effects disclosed above are achievable utilizing the Bronsted-Lowrey acid (i.e. protic acid) salt of the above described compounds.

Synthesis of the salt: Synthesis of the salts from the free amine compounds is simple and should be well known and within the skill of a person of ordinary skill in the art. In one method the salt is formed in situ within a fully formulated mud by the addition of the acid directly to the mud. Alternatively the amine compound may be neutralized first with acid and then the salt added to the mud. When conducting the neutralization reaction between the amine compound and the acid compound either concentrated or diluted acid may be used. When concentrated acid is utilized, typically a slurry of the salt is formed. When the acid is diluted in water, an aqueous solution containing the amine salt is formed. The following table provides exemplary data of the viscosities of the product resulting from the neutralization of Jeffamine D-230 with various acids to the specified pH values.

Viscosity (centipoises) Viscosity (centipoises) Acid at pH 9.5 at pH 10.5 Hydrochloric  275 cps  98 cps Nitric  610 cps 120 cps Acetic 1425 cps  33 cps Citric 2000 cps 180 cps Phosphoric slurry slurry

In the above examples partial neutralization has been carried out by adding acid to the amine so as to achieve the desire pH value. Alternatively, one or more equivalent of acid may be mixed with the amine compound thus bringing the pH of the resulting solution to a neutral value of 7 or a slightly acidic value. In such instances, the salt of the amine compound may be recovered using conventional methods known to one of skill in the art.

Drilling Fluid/Mud Formulation: The formulation of a drilling fluid or mud that includes the above compounds is, except for the inclusion of the above compounds, conventional. An illustrative base mud formulation is given in the following table,

Component Amount Water 278 Sea Salt 11.91 Salt 70.91 Encapsulator 2.00 Polypac UL 2.00 Duo-Vis 0.73 Barite 117.7 Rev Dust 25.0

The illustrative mud formulations of the present invention utilize the above mud formulation and include about 2-3% by weight of shale inhibitor. The shale inhibitor is added before the addition of the Rev Dust or any other clay components.

The above drilling fluid formulation containing a variety of shale inhibitors exhibited the following properties:

D-230 HCl JLB-352 HCl JLB-354 HCl Shale Inhibitor salt salt salt pH 9.8 9.8 9.8 Rheology @ 120° F. 600 92 109 110 300 57 69 70 200 44 54 54 100 28 35 34  6 7 9 8  3 5 7 7 Gels 10 Mm. 6 8 8 10 Sec. 9 11 11 PV 35 40 40 YP 22 29 30 API-Fluid Loss 4.2 ml 3.4 ml 3.6 ml

In the above table JLB-352 is a ethylene glycol ether diamine and JLB-354 is a propylene glycol ether diamine available from Champion Chemicals.

Upon review of the above data, one of skill in the art should understand and appreciate that the above formulation exhibit properties that make them useful as drilling fluids.

Hot-Rolling Dispersion: The following experiments were carried out to illustrate the shale inhibition properties of the compounds of the present invention. A hot-rolling dispersion test was conducted using samples of Arne shale, Foss Eikeland shale and actual shale drilling cutting recovered from a well in the field. The shale samples were added to the fully formulated mud including shale inhibitor and Rev Dust was added 10 g of cuttings in a one-barrel equivalent of laboratory prepared muds. The resulting mixture was hot rolled for 16 hours at 150° F. After rolling, the remaining shale cuttings were screened from the drilling mud using a US 20 mesh screen and washed clean of drilling fluid with 10% potassium chloride aqueous solution. After drying the samples as weighed and the percentage of recovered shale is calculated. The exemplary results are given in the following table:

Shale Inhibitor Arne shale Foss Eikeland field cuttings D-230 HCl salt 95 97 96 JLB-352 HCl salt 96 97 94 JLB-354 HCl salt 96 97 95

Upon review of the above data one of skill in the art should understand and appreciate that the amine salts of the present invention exhibit shale inhibition properties that make them useful as shale inhibition agents in drilling fluids.

Slake Durability Test: The Slake Durability apparatus consists of a 1 mm mesh brass cage rotated at 40 rpm in plastic tanks. Approximately 50% of the cage is submerged in about 350 ml of test fluid. Place 25-30 g of test cuttings into a Slake Durability cage and place into a tank filled with 1 barrel equivalent of the test fluid and rotate for 4 hours. Upon completion of the rolling process, the cage is removed from the tank and dipped into a bath of 105 potassium chloride to rinse off any excess test fluid from the cuttings. The cuttings are then removed from the cage, dried at 220° F. and weighed. The percentage of cuttings recovered is calculated with a higher recover percentage indicating the effectiveness of the shale inhibition agent. Exemplary data is given in the following table.

Arne shale Foss Eikeland field cuttings Shale Inhibitor (% recovered) (% recovered) (% recovered) D-230 HCl salt 49 55 94 JLB-352 HCl salt 27 60 91 JLB-354 HCl salt 43 55 94

Upon review of the above data one of skill in the art should understand and appreciate that the amine salts of the present invention exhibit shale inhibition properties that make them useful as shale inhibition agents in drilling fluids.

Example 9

The following tests were conducted to demonstrate that the shale inhibiting effects disclosed above are achievable utilizing a variety of Bronsted-Lowrey acid (i.e. protic acid) salt of the above described compounds. Synthesis of the amine salt was carried out as previously disclosed above. Fresh water was utilized as the base fluid in this example.

Hot-Rolling Dispersion: The following experiments were carried out to illustrate the shale inhibition properties of the compounds of the present invention. A hot-rolling dispersion test was conducted using samples of Oxford shale, Foss Eikeland shale and actual shale drilling cutting recovered from a well in the field. To 350 ml freshwater including 10.5 g of shale inhibitor was added 10 g of cuttings. The resulting mixture was hot rolled for 16 hours at 150° F. After rolling, the remaining shale cuttings were screened from the base fluid using a US 20 mesh screen and washed clean of base fluid with 10% potassium chloride aqueous solution. After drying the samples, they were weighed and the percentage of recovered shale was calculated. The exemplary results are given in the following table:

Shale Inhibitor Oxford shale Foss Eikeland shale field cuttings D-230 acid salt (% recovered) (% recovered) (% recovered) Hydrochloric acid 89.0 45.0 43.9 Acetic acid 88.0 72.4 47.6 Citric acid 87.0 78.0 30.9 Nitric acid 87.6 69.1 45.7 Phosphoric acid 87.8 69.1 42.6

Upon review of the above data one of skill in the art should understand and appreciate that the amine salts of a variety of protic acids illustrative of the present invention exhibit shale inhibition properties that make them useful as shale inhibition agents in drilling fluids.

In view of the above disclosure, one of skill in the art should understand and appreciate that one illustrative embodiment of the present invention includes a water-base drilling fluid for use in drilling wells through a formation containing a shale which swells in the presence of water. In such an illustrative embodiment, the drilling fluid comprising, an aqueous based continuous phase, a weight material, and a shale hydration inhibition agent. The shale hydration inhibition agent should have the general formula: H₂N —R—{OR′}_(x—Y.[H) ⁺B⁻]_(d) in which R and R′ are alkylene groups having 1 to 6 carbon atoms and x has a value from about 1 to about 25. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group. The B⁻ anion is the conjugate base of an acid, preferably a Bronsted-Lowrey protic acid. The value of d depends upon the extent of protonation of the amine compound, however, generally the value will be equal to or less than 2. Illustrative examples of suitable protic acids include: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumaric, glycolic, lactic, citric and combinations of these.

The shale hydration inhibition agent should be present in sufficient concentration so as to reduce the swelling and hydration of shale.

One aspect of the present illustrative embodiment, x has an average number between about 1 and about 25 and preferably about 1 to about 10. In another aspect of the present illustrative embodiment, R and R′ are alkylene groups having a different number of carbon atoms. The illustrative drilling fluid should be formulated so as to include a shale hydration inhibition agent that is characterized by low toxicity and compatibility with anionic drilling fluid components. It is preferred that in the present illustrative embodiments that the aqueous based continuous phase may be selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof. Further the illustrative drilling fluids may contain a fluid loss control agent selected from the group including organic polymers, starches, and mixtures thereof. An encapsulating agent may also be included and preferably the encapsulating agent may be selected from the group organic and inorganic polymers and mixtures thereof. The illustrative drilling fluid may include a weight material selected from: barite, hematite, iron oxide, calcium carbonate, magnesium carbonate, magnesium organic and inorganic salts, calcium chloride, calcium bromide, magnesium chloride, zinc halides and combinations thereof.

Another illustrative embodiment of the present invention includes a water-base drilling fluid for use in drilling wells through a formation containing a shale clay which swells in the presence of water. In such an illustrative embodiment, the drilling fluid may include: an aqueous based continuous phase, a weight material, and a shale hydration inhibition agent selected from the group: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d) H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂.[H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) and mixtures of these. The B⁻ moiety is the conjugate base of a protic acid, preferably selected from the group of Bronsted-Lowey acids including hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. The value of d will depend upon the equivalents of acid present as well as the pKa of the acid, pKb of the amine and pH of the mud formulation. However, generally d has a value equal to or less than 2. The hydration inhibition agent should be present in the drilling fluid in sufficient concentrations to reduce the swelling of the clay.

In one preferred illustrative embodiment, the aqueous based continuous phase may be selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof. The illustrative drilling fluid may further contain a fluid loss control agent selected from organic polymers, starches, and mixtures thereof.

In addition, the illustrative drilling fluid may further contain an encapsulating agent selected from organic and inorganic polymers and mixtures thereof. It is preferred that the weight material in the present illustrative embodiment be selected from barite, hematite, iron oxide, calcium carbonate, magnesium carbonate, magnesium organic and inorganic salts, calcium chloride, calcium bromide, magnesium chloride, zinc halides and combinations thereof.

The present invention also encompasses a method of reducing the swelling of shale clay encountered during the drilling of a subterranean well, In one illustrative embodiment, the method includes: circulating in the subterranean well during the drilling of said well a water-base drilling fluid that includes: an aqueous based continuous phase and a shale hydration inhibition agent having the formula: H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d) in which R and R′ are alkylene groups having 1 to 6 carbon atoms and x is a value from about 1 to about 25 and preferably from about 1 to about 10. The Y group should be an amine or alkoxy group, preferably a primary amine or a methoxy group. The B⁻ moiety is the conjugate base of a protic acid, preferably selected from the group of Bronsted-Lowey acids including hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. The value of d will depend upon the equivalents of acid present as well as the pKa of the acid, pKb of the amine and pH of the mud formulation. However, generally d has a value equal to or less than 2. As noted previously, the shale hydration inhibition agent should be present in sufficient concentration to reduce the swelling of the shale clay. The shale hydration inhibition agent may be further characterized by low toxicity and compatibility with anionic drilling fluid components.

Another illustrative embodiment of the present invention includes a method of reducing the swelling of shale clay encountered during the drilling of a subterranean well, in which the method includes: circulating in the subterranean well a water-base drilling fluid. The fluid of the illustrative method is formulated to include: an aqueous based continuous phase, a weight material, and a functionally effective concentration of a shale hydration inhibition agent selected from: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d) H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂.[H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) and mixtures of these compounds. The B⁻ moiety is the conjugate base of a protic acid, preferably selected from the group of Bronsted-Lowey acids including hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. The value of d will depend upon the equivalents of acid present as well as the pKa of the acid, pKb of the amine and pH of the mud formulation. However, generally d has a value equal to or less than 2. The shale hydration inhibition agent should be present in a concentration sufficient to reduce the swelling of the shale clay. It is preferred within this illustrative method that the aqueous based continuous phase may be selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof.

While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the process described herein without departing from the concept and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention as it is set out in the following claims. 

1. A water-base drilling fluid for use in drilling wells through a formation containing a shale which swells in the presence of water, the drilling fluid comprising: an aqueous based continuous phase; a weight material; and a shale hydration inhibition agent having the formula: H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d) wherein R and R′ are alkylene groups having 1 to 6 carbon atoms and x is a value from about 1 to about 25, and and Y is an amine or alkoxy group and B⁻ is the conjugate base of an acid and d is a value equal to or less than 2 wherein the shale hydration inhibition agent is present in sufficient concentration to reduce the swelling of the shale.
 2. The drilling fluid of claim 1 wherein x has an average number between about 1 and about
 10. 3. The drilling fluid of claim 1 wherein R and R′ are alkylene groups having a different number of carbon atoms or a same number of carbon atoms.
 4. The drilling fluid of claim 1 wherein H⁺B⁻ is a protic acid selected from the group consisting of inorganic acids and organic acids.
 5. The drilling fluid of claim 1 wherein B⁻ is the conjugate base of an acid selected from the group consisting of: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these.
 6. The drilling fluid of claim 1 wherein the shale hydration inhibition agent being further characterized by low toxicity and compatibility with anionic drilling fluid components.
 7. The drilling fluid of claim 1 wherein the aqueous based continuous phase is selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof.
 8. The drilling fluid of claim 1 wherein the drilling fluid further contains a fluid loss control agent selected from the group consisting of organic polymers, starches, and mixtures thereof.
 9. A water-base drilling fluid for use in drilling wells through a formation containing a shale clay which swells in the presence of water, the drilling fluid comprising an aqueous based continuous phase a weight material, and a shale hydration inhibition agent selected from the group: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d) H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂.[H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) wherein B⁻ is the conjugate base of a protic acid and d is a value equal to or less than 2, and mixtures of these, wherein the hydration inhibition agent is present in the drilling fluid in sufficient concentrations to reduce the swelling of the clay.
 10. The drilling fluid of claim 9 wherein the aqueous based continuous phase is selected from: fresh water, sea water, brine, mixtures of water and water soluble organic compounds and mixtures thereof.
 11. The drilling fluid of claim 10 wherein the drilling fluid further contains a fluid loss control agent selected from the group consisting of organic polymers, starches, and mixtures thereof.
 12. The drilling fluid of claim 11 wherein the drilling fluid further contains an encapsulating agent selected from the group consisting of organic and inorganic polymers and mixtures thereof.
 13. The drilling fluid of claim 11 wherein B⁻ is the conjugate base of a protic acid selected from the group consisting of: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these.
 14. A method of reducing the swelling of shale clay encountered during the drilling of a subterranean well, the method comprising: circulating in the subterranean well a water-base drilling fluid including: an aqueous based continuous phase and a shale hydration inhibition agent having the formula: H₂N—R—{OR′}_(x)—Y.[H⁺B⁻]_(d) wherein R and R′ are alkylene groups having 1 to 6 carbon atoms and x is a value from about 1 to about 25, and Y is an amine or alkoxy group, and B⁻ is the conjugate base of a protic acid and d is a value equal to or less than 2 wherein the shale hydration inhibition agent is present in sufficient concentration to reduce the swelling of the clay.
 15. The method of claim 14 wherein x has a value of about 1 to about
 10. 16. The method of claim 15 wherein B⁻ is the conjugate base of a protic acid selected from the group consisting of: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these.
 17. A method of reducing the swelling of shale clay encountered during the drilling of a subterranean well, the method comprising: circulating in the subterranean well a water-base drilling fluid including: an aqueous based continuous phase, a weight material, and a functionally effective concentration of a shale hydration inhibition agent selected from the group: H₂N—CH₂CH₂—O—CH₂CH₂—NH₂.[H⁺B⁻]_(d) H₂N—CH₂CH₂CH₂—O—CH₂CH₂—O—CH₂CH₂CH₂—NH₂.[H⁺B⁻]_(d) NH₂—CH₂—CH(CH₃)—(O—CH₂—CH(CH₃))₈—O—CH₂—CH₂—OCH₃.[H⁺B⁻]_(d) wherein B⁻ is the conjugate base of a protic acid and d is a value equal to or less than 2, and mixtures of these compounds, and wherein the shale hydration inhibition agent being present in a concentration sufficient to reduce the swelling of the clay.
 18. The method of claim 17 wherein B⁻ is the conjugate base of a protic acid selected from the group consisting of: hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, boric, perchloric, formic, acetic, halogenated acetic, propionic, butyric, maleic, fumeric, glycolic, lactic, citric and combinations of these. 